SEA02LA187

During cruise flight, the aircraft began to lose oil pressure, and the propeller rpm stopped responding to the position of the propeller governor control lever. Eventually the engine oil pressure dropped to zero, and the pilot elected to attempt a forced landing on a country road. Although the touchdown was successful, during the landing roll, the aircraft's wings collided with mailboxes mounted on steel poles situated immediately adjacent to the side of the road. It was later determined that both compression rings on the number four piston had failed (fractured), and that a portion of the piston outer wall near the piston dome had eroded away allowing loss of a majority of the engine's oil through the engine exhaust system.

On September 30, 2002, approximately 1630 mountain daylight time, the wings of a Mooney M20J, N4232H, collided with mail boxes mounted on steel posts during the landing roll after the pilot successfully executed a forced power-off landing on a country road. The private pilot and his passenger were not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Walker Field, Grand Junction, Colorado, about two hours earlier, was being operated in visual meteorological conditions. The ELT was not activated.

According to the pilot, while en route, the aircraft began to lose oil pressure and eventually the propeller failed to respond correctly to the movement of the propeller rpm governor control lever. Eventually the oil pressure dropped to zero, and the pilot elected to make an emergency landing on a country road. Although the pilot was able to maneuver the aircraft to a successful touchdown on the road he selected, during the landing roll, the wings of the aircraft collided with mail boxes situated immediately adjacent to the edge of the road.

A post-accident inspection of the engine revealed that both compression rings on the number four piston had fractured, and a 3/8 inch wide section of the piston surface had been eroded away. The eroded area extended from the land of the bottom compression ring, through the land of the top compression ring, to within 1/16 inch of the piston dome. The depth of the erosion was approximately 1/8 inch (level with the bottom surface of the ring land). In addition, according to the FAA inspector who looked at the engine after the number four cylinder was removed, except for a small residual amount, the engine had lost all of its oil supply, and the number three connecting rod bearing was beginning to extrude from between the rod end and the crankshaft journal. The investigation also revealed that the number four cylinder exhaust pipe was contaminated with both oily soot and a coating of unburned oil. In addition, the fuselage skin in the area aft of the exhaust pipe for the number two and number four cylinders was coated with what appeared to be relatively fresh oil.